The need for efficient solar energy collectors has become extremely important with the advent of conservation of heat-producing natural resources such as gas and oil. However, while solar collectors now have been produced for converting solar energy to useable heat, they are relatively expensive and in fact are so expensive that it is questionable whether they can be economically substituted for or make supplemental to conventional heat-producing systems.
Solar collectors of one well known type usually utilize a boxlike housing containing a solar radiation-absorbing panel covered by a radiation-transparent glazing, usually glass or plastic sheeting. Metal piping is mounted on the under side of the panel in some manner so that when the panel is heated by impinging solar radiation, the resultant heat will be transferred to a fluid which is circulating through the piping. The piping, usually copper tubing, is expensive and must be supported in efficient heat-transfer relation to the panel.
For example, in U.S. Pat. No. 3,039,453 there is disclosed a solar collector which comprises a plate or panel which has in its back side a number of parallel grooves which may be formed by crimping. Flexible tubing is snapped into the grooves and heat from the panel is transferred to fluid which circulates through the tubing. However, it has proved to be difficult to efficiently transfer heat from the panel to the fluid in such a structure because often the tubing is not retained in good thermal contact with the walls of the grooves throughout their lengths.
One method of overcoming the problem is taught by U.S. Pat. No. 3,898,979 which discloses a somewhat similar structure with the addition of a heat-conducting material between the tubing and the walls of the grooves, which material is intended to bond the adjacent wall and tubing surfaces together and provide complete contact between the surfaces throughout their lengths and thereby enhance the transfer of heat to the fluid. This solution, however, requires a relatively costly manufacturing operation and will not guarantee success.
A further method of retaining a flexible tubing in thermal contact with a solar radiation absorbing plate is also disclosed in U.S. patent application Ser. No. 689,608, filed May 24, 1976 and assigned to the assignee of the present invention. In said application the panel is formed of two or more sections disposed in a common plane in side-by-side relation with their edges being provided with curved digits or fingers, the fingers of one panel interfitting with the fingers of an adjacent panel to from a substantially solid tubular configuration within which a tubing is disposed. The fingers thus grip the tubing and are in good thermal contact with it without requiring an intermediate bond. However, the panels must be stamped to form the fingers and subsequently assembled together and with a tubing. This is efficient but not the most economical construction.